Adhesive material



Patented June 5, 1945 ADHESIVE MATERIAL Y Emile Pragofi, Jr., Wilmington, DeL, assignor to Hercules Powder Company, Wilmington, inlet, a corporation of Delaware l lo Drawing. Application iiune 8, mid, Serial No. erases iii Claims.

This invention relates to adhesives and more particularly to adhesives of the rubber base, pressure-sensitive type useful in the preparation of adhesive tapes, masking tapes, and theJilre. it also relates to adhesive tapes prepared with the adhesives.

Pressure-sensitive adhesives of the type utilized in adhesive tape, masking tape, Scotch tape, and the like, have the property of forming an adherent bond without the use of heat or solvents. At the same time, they are removable with the tape on which they are applied without raarring or leaving soiled the surface which they have covered. Adhesives of this type have a very particular set of requirements. Necessarily, they combire a high degree of tack with carefully controlled cohesion and toughness within the adhesive mass.

Most pressure sensitive adhesives are based on rubber compositions in which the rubber is modified by a resin. The rubber provides the necessary cohesion but must be modified to develop in combination the desired plastic properties and,

tackiness. The modification must lead to the desired plasticity and tack without making the composition mushy or imparting to the composition a tendency to string when the adhesive is removed from a surface as when adhesive tape is pulled from a roll. Heretofore, the resinous modifier has been a coumarone-indene resin, rosin, ester gum or hydrogenated rosin.

Pressure-sensitive rubber adhesives made with these modifiers have been unsatisfactory in two chief respects. First, the adhesive material has, in many cases, aged very poorly in that the ma- ,ester gum, and has been alleviated to some extent where such resins inhydrogenated form have 'terial became tough and hard with loss of the been employed. Second,with all rosins heretofore utilized, the initial tack of the adhesive has been less than desired for a given state of cohesion. It will be appreciated that tackiness can be increased to some extent by softening the plastic mass but to obtain the desired high state of tackiness would require softening to an extent at which the mass becomesmushy or stringy due to loss of internal cohesion, thus leading to a condition in which adhesives remain on a surface when attempts are made to remove adhesive tape, mashing tape, and the lllte. It has, therefore, been desirable to bring about an improvement in tacln'ness without decreasing the cohesion of the mass materially.

in accordance with this invention, pressuresensitive compositions which are stable with age, which are highly tacky, and which are of satis factory cohesiveness with respect to given taclriness, are obtained by compounding rubber with a rosin derivative containing an appreciable proportion of dehydrogenated rosin acid groups in a ratio at rubber to such a rosin derivative between about to to and about to 2.0 and including in the composition a softener for the rubber-rosin derivative mixture in an. amount which is sumcient to develop, bring out, or increase the taclrirress thereof but which is insum: cient to reduce the property of cohesion to an extent in which the final composition is mushy or in which it strings upon being pulled away from a surface with which it has been in contact. The rosin derivative containing an appreciable proportioh of dehydrogenated rosin acid groups is a dehydrogenated rosin acid itself, de-

hydrcgenated rosin, a disproportioned rosin acid,

Hyex rosin, a. Hyex" rosin acid, disproportionated rosin, pseudopimaric acid,pyroabletic acid, a mixture of such rosins orof such acids, an ester of one or more of these resins or of these acids or a, mixture of esters of the rosins or of the acids.

In accordance with this invention, pressuresensitive adhesive tape and adhesive sheeting is obtained by coating a pressure-sensitive adhesive of the type described on sheeting, webs or strips of flexible materials such as cloth, paper, and films of regenerated cellulose, cellulose derivatives, rubber hydrochloride, and the like.

The adhesive compositions in accordance with this invention and adhesive sheeting prepared therefrom may best be described by specific embodiments thereof in the examples which follow. The compositions were prepared by breaking down crepe rubber for 20 minutes at F. on a, two-roll mill, using 75 cuts and turnbacks and then sheeting. Weighed portions of the rubber were then worked on the rolls for 5 minutes at friction heat (150 F), the rosin derivative added in 10 minutes of rolling, and the tiller in 10 more minutes, Softener was milled in last over a period of 5 minutes. Compositions of Table I illustrate examples found suitable; parts are by *bon tetrachloride and drying for 48 hours were tested for toughness of bond. Tapes one by two inches of light duck were rolled into the 0.005

' inch dried films by rolling five times with a one weight. 5 kilogram weight. The bond was aged 48 hours Table I Example 1 2 a 4 5 o 7 s 9 11 12 H exrosln 20 Gyce lester of Eye: rosi Diethg ene glycol ester of Eye: rosin Dehy ogenatsd rosin (rosin heated with iodine)-.. Glyceryl ester of dehydrogensted rosinm- 50 Pseudoplmaric acid Hyex rosin methyl ester 30 Orepernhhnr 80 50 50 50 25 100 70 Butylr h r 50 Lanolin 2a 1o 20 so 40 20 2o Reflnedminereloil 20 l 30 hydrogenated cottonseed oil l zinc oxide 12 2o 10 1o 15 1o 25 15 Lithopone so at 35 so as 45 as so 75 as The compositions were applied in benzol soluat 70 F. and 65% relative humidity. The force tion, at a. concentration giving a readily workable in pounds required to pull the tape from the glass consistency, to paper, to regenerated cellulose and is recorded in Table III. to muslin. For example, the compositions I of Examples 2, 3, 4, '7, 8 and 10 were dissolved in Table 'Strength of bond 60 parts of benzene and applied as'coatings.

Muslin tapes so prepared were exposed 24 hours ttfffifi ttfi fitii" to ultraviolet light. Tack was retained in all Rosin derlgativeused cases. There was only slight darkening of the 20% 30% 40% composition. Tapes coated with like compositions, using rosin instead of the rosin derivative 35 Hydrogenated mm 23 v 21 18 indicated compounds discolored considerably and Eye! r0511 30 24 9 lost nearly all tack. Aging for 25 days in open air give'similar but somewhat less drastic results. It will be noted that the Hyex rosin gave bonds Further examples are given in Table II with of considerably greater strength than the hydrotest results giving comparisons with similar genated rosin; yet, as shown in Table II, th compositions made with hydrogenated rosin. In tackiness was greater. all examples of Table II, 50 parts of the rosin It has been found that the rubber utilized in derivativespecified was milled with 50 parts of the compositions of the present invention may be crepe rubber, 12 parts of zinc oxide and 38 parts a natural rubber in the form of crepe, smoked g lithopone in t manner described fur t sheets, latex (usually coagulated before use), or vious examples. Lanolin was used as the softit may be a synthetic rubber such as those derived ener and varied as indicated. Tackiness by peneby the polymerization p ymerization with trometer is in readings of thousandths of an inch modifiers of butylene, bu ai ne, buta-diene de-' using 100 grams weight on a Roberts No. 2 rivatives, and the like to form rubbery elastomers. needle for 5 seconds in a. standard penetrometer. Preerably, D g; Crepe rubber s utilized. Pref- I era ly, the ru er is broken down by milling on Table by m the usual rubber rolls to some extent before it i v is compounded with the other ingredients of the gg g g ggiggg g ggggf composition. However, it has been found that Rosin demameuaed ative less milling of the rubber is necessary than is usually required to obtain the desired compati- 0% 20% 30% 40% bility with the resinous component. I

The rosin derivative which is utilized to co- Hydrogenated rosin 62 46 53 89 act with the rubber to bring about a desir ble gge fgg gggfggffi fifffiffffi fif fff; 34 107 20g 304 state of plasticity and to bring about tackiness Hyexros n 33 99 124 167 in the mass is characterized by an appreciable proportion of dehydrogenated rosin acid groups. It willbe noted that with equal parts of resin The various derivatives which have been menand rubber as in Table II compositions, the tack tioned and which are illustrated in the examples is relatively low. Softener has little effect until are so characterized. By dehydrogenated rosin in very large amounts when using hydrogenated acid is meant a rosin acid having at least two rosin. However, the softener is very effective less hydrogen atoms per molecule than abietic with dehydrogenated rosin and provides a very acid, sapinic acid, or pimaric acid, all of which much tackier composition than the corresponding have the formula C2oH30O2. The dehydrogenated hydrogenated rosin composition in every case. rosin acid group may be present in the form of Films of the various compositions on glass plates the carboxylic acid or in the form of an ester of tested for tack by merely touchinggave results the carboxylic acid. In most cases, the dehydroin line with the penetrometer tack readings. genated acid or acid group will contain two less Films on glass cast from solutions of composihydrogen atoms than the rosin acid (abietic, tions used in Table II in equal quantities of car- 7e sapinic. Pimaric, etc.) and will, thus, be ch herein and in the claims.

acme" acterized by one additional double bond. However, it may contain less hydrogen.

It has been iound that the dehydrogenated rosin acid group leads to a highly stable acmesive possibly resulting from a protective action in combination with a high stabillw for the group itself. In addition, it leads to an improved tackiness which is believed to be brought about by an improvement in compatibility of the group with rubber as compared with other resins such as rosin, ester gum, hydrogenated rosin, and the like. To obtain the desired properties, the rosin derivative utilized should contain at least 30% by weight of dehydrogenated rosin acid groups. This proportion is based on the total content of rosinyl groups present so "that in the case oi esters the percentage represents the quantity of the acid groups on the basis oi the acid groups present in the esters, whether esterified or not; the proportion of dehydrogenated rosin acid groups may be determined as hereinafter specifled.

It will be appreciated that pure or substantially pure dehydrogenated rosin acids or their esters may be employed. However, it is not essential that the rosin derivative consist entirely of such acids or their esters. Dilution to the extent previously indicated with rosin acids or rosin acid esters is possible but it will be appreciated that the greater the content of normal rosin acids, the lower will be the stability of the product. Dilution with hydrogenated rosin acids or their esters is less serious in that such materials age reasonably well. However, the beneficial results of the present invention are greatest with the least dilution of the dehydrogenated rosin acid groups.

Rosin acids in the form of relatively pure acids or in the form of rosin itself (either gum or wood rosin may be used) may be converted into dehydrogenated derivatives for use in the present compositions by several methods. For example, the rosin acid or esters thereof may be heated for one to two hours at 156 to 200 C. with a dehydrogenating catalyst such as iodine or sulphur, in a quantity 0.5 to oi the rosin acid. Alternatively, the resin, rosin acid, or ester, may be dehydrogenated or disproportionated or both reactions may be carried out by heating for one to four hours at 180 to 245 C.

with a hydrogenation catalyst such as nickel, platinum, or palladium, in suspension, or an inert support, or on an activated support such as activated carbon, activated alumina, activated silica gel, and the like, under conditions at which known as Hyex" compounds and the reaction by which they are produced as the Hyex" reaction and they will be referred to in this manner Pyroabietic acid, which is rich in dehydroabietic acid, is also a suitable rosin derivative for the adhesives of the present invention. It may beprepared by heating a resin or a rosin acid for one to four hoursat 260 to 315 C. The pseudopimaric acid whichis described in U. S. Patent No. 2,072,628, is similarly suitable.

It will be noted that Examples 1, 2, 3, 6, 8, and 10-11 illustrate the use oi dehydrogenated rosin acids. However, as shown by Examples 4, 5, 9 and 12, esters 01 such acids are equally suitable. The esters may be esters oi! polyhydric alcohols such as ethylene glycol, diethylene glycol, glycglycerol tripropionate, and the litre.

erol, diglycerol, erythritol, pentaerythritol, dipentaerythritol, sorbitol. etc, or they may be esters of monohydric alcohols such as benzyl, methyl, ethyl, butyl, lauryl, and methoxyethyl alcohol. it

The rosin derivative containing the dehydrogenated rosin acid groups will be compounded with the rubber in a ratio of the rubber to the rosin derivative between about so to 60 and about to 20, preferably between 45 to 55 and do to 40. The ranges are required to obtain the desired combination of tack and cohesion after addition of softeners.

The rosin derivative containing dehydrogenated rosin acid groups, has, to a limited extent, a plasticizing effect upon the rubber of the composition. However, its chief function is to form a unique plastic structure with the rubber and to bring about the desired tackiness in this structure. For .some purposes, the tacky plastic of rubber and the rosin derivative maybe used without iurther modification. However, it has been found that the improved high tack desired requires modification with a softener compatible with the rubber-rosin derivative plastic. It has been found that softeners greatly increase the tacklness of such compositions. Suitable softenors which have been found satisfactory in the present compositions are, for example, lanolin, mineral oil, dibutyl phthalate, hydrogenated cottonseed oil, hydrogenated methyl abietate,

The quantity of softener added is a quantity sumcient to increase the tackiness of the composition, but less than a quantity which brings about a mushy condition in which portions of adhesive stick when the adhesiveis pulled away from a surface to which it is temporarily bonded; and less than a away from a surface with which it has been in contact, as, for example, when a masking tape is stripped after use or, ior example, when an adhesive tape is unrolled. It has been found at least a quantity of 10% by weight of softener is required. At 20% and above, the composition is markedly superior in tack to unsoitened compositions and also to softened compositions in which rosin or hydrogenated rosin are used. Preferably, between 20% and dim; oi softener is used. More than about 50% leads to a mushy plastic. Softener percentages are of the combined weight of the rubber and the rosin derivative used.

Where desired, the adhesive compositions in accordance with this invention may contain inert solid filler such as zinc oxide, barium sulfate, antimony oxide,- lithopone, clay, chalk, and the like. The inert solid fillers are not essential but they extend the adhesive and thereby lower its cost and, in addition, in some cases, they render the composition firmer and shorter so that tendency to strin is decreased. Fillers'will ordinarily' comprise less than 45% by weight of the entire non-volatile contents of the adhesive composition. Waxy substances may also be included if desired. For example, paramn, carnauba, wax,

of the two-roll type. Usually, the rubber will be broken down, for example, fo 20 to 35 minutes at the natural friction temperature of the mass and the other components'will then be rolled. Usually, the temperature is held between about 60 and about 100 C. during the milling operation. It should be kept in mind that excessive periods of milling reduce the cohesive strength contributed to the plastic mass by the rubber and, hence, milling should be limited to the shortest period practical for bringing about a uniform dispersion of the components of the mixture. In

preparing'the adhesives according to the present invention, the rubber is desirably milled for periods shorter than would be necessary using other resins (such as rosin, estergum, hydrogenated rosin, cournarone resins, etc.) under like conditions.

The adhesive composition may be applied to suitable sheeting such as cotton sheeting, paper,

creped paper, cellulose and cellulose derivative sheeting, and the like, by spreading in the molten state, by calendering in the semi-molten state, by coating in the form of solutions and so]- vents such as, for example, benzene, toluene,

ill

butyl acetate, and carbon tetrachloride, or by other methods of spreading.

The adhesive compositions and adhesive sheeting prepared therewith in accordance with, this invention have the advantage of retaining tackiness, and retaining the initial combination of toughness and softness of the material over long periods of time, as compared with similar prod nets in which rosin, ester gum, coumarone resins, and the like are utilized instead of the rosin derivative rich in dehyrogenated rosin acid groups. This result is thought to be in part due to the stability of the deyhdrogenated rosin acid group, to a protective action on the rubber of this group, and to a modification of the nature of the plastic mass due to compatibility diiferences. The dehydrogenated rosin acid groups contain less hydrogen than the normal rosin acid groups and, in that sense, are more unsaturated. However, they exhibit less tendency to oxidize and, in general, will have a thiocyanogen number of -10 as compared with 90-100 for the normal rosin acid.

The products according to this invention exhibit high tackiness for a given cohesion, (and in a rosin derivative is readily determined in the following manner. One hundred grams of the rosin derivation are dissolved in 200 cubic centimeters of carbon tetrachloride, cooled to 0 C.. and 500 cubic centimeters of 95% of sulfuric acid are added with agitation. The mixture is stirred at 05 C. for one hour and 200 cubic centimeters more carbon tetrachloride are stirred in with one liter of ice. The precipitate which forms is illtered off and Washed with a small amount of cold water. The precipitate is then added to one liter of water, boiled, acidified with hydrochloric acid, and then cooled overnight at 0-3 C. It is then filtered off, washed with a small amount of cold water and dried at 70 C'. The sulfodehydroabietic acid resulting is then hydrolyzed by treatment with 60% sulfuric acid added in the proportion of 660 cubic centimeters for each 30 grams high cohesion for a given tackiness) as compared with similar compositions in which rosin, ester gum, hydrogenated rosin, eoumarone resin, and the like, are utilized. This efi'ect is thought to be brought about by a higher compatibility with rubber and is enhanced by the fact that less milling of the rubber is required. In addition, less added softener is required to raise the tack to a given level and this, in turn, permits more tackiness to be developed without difliculties due to stringing and mushiness of .the resulting adhesive.

The content of dehydrogenated rosin groups my copending application, Serial No. 265,521, filed April 1, 1939, now Patent No. 2,285,458, June 9, 1942.

What I claim and desire to protect by Letters Patent is:

1. An age-resistant, highly tacky, pressure-sensitive adhesive comprising rubber, a rosin derivative containing appreciable dehydrogenated rosin acid groups, said derivative being selected from the group consisting of dehydrogenated rosin acids, dehydrogenated rosin, rosin which has undergone interand intramolecular rearrangement in such manner that the ethylenic unsaturation thereof has been reduced, said rearrangement having been effected by treatment of the rosin with a hydrogenation catalyst in the absence oi added substances capable of reducing the degree of unsaturation thereof, rosin acids which have undergone interand intramolecular rearrangement in such manner that their ethylenic un-- saturation has been reduced, said rearrangement having been effected by treatment of the material with a hydrogenation catalyst in the absence of added substances capable of reducing the degree of unsaturation, pseudopimaric acid, pyroabietic acid, mixtures of the said rosins and acids, esters of the said rosins and acids, and mixtures of the said esters, the ratio of rubber to said rosin derivative being between 40:60 and :20, and

lanolin in an amount between about 10% and about 50% of the combined weight of the rubber and said rosin derivative.

2. An age-resistant, highly tacky, pressure sensitive adhesive comprising rubber, dehydrogenated rosin, the ratio of rubber to dehydrogenated rosin being between 40:60 and 80:20, lanolin in an amount between 10% and 50% of the combined weight of the rubber and dehydrogenated rosin, and zinc oxide.

3. An age-resistant, highly tacky, pressuresensitive adhesive tape comprising cotton textile sheeting coated with an adhesive comprising rubber, a rosin derivative containing appreciable dehydrogenated rosin acid groups, said derivative being selected from the group consisting of'dehydrogenated rosin acids, dehydrogenated rosin, rosinwhich has undergone interand intramolecular rearrangement in such manner that the I ethylenic unsaturation thereof has been reduced,

said rearrangement having been efiected by treatment of the rosin with a hydrogenation catalyst in the absence of added substances capable of reducing the degree of unsaturation thereof, rosin acids which have undergone interand intramolecular rearrangement in such manner that their ethylenic unsaturation has been reduced, said rearrangement having been effected by treatment of the material with a hydrogenation catalyst in the absence of added substances ca- .pable of reducing the degree of unsaturation,

pseudopimaric acid, pyroabietic acid, mixtures of the said resins and acids, esters of the said rosins and acids, and mixtures of the said esters, the ratio of rubber to said rosin derivative being between 40:60 and 80:20, and lanolin in an amount between about and about 50% of the combined weight of the rubber and said rosin derivative.

4. An age-resistant, highly tacky, pressuresensitive adhesive comprising rubber and dehydrogenated rosin, the ratio of rubber to the dehydrogenated rosin being between 40:60 and 80:20, and a softener for the rubber-rosin derivative composition selected from the group consisting of lanolin, mineral oil, lycerol tripropionate, dibutyl phthalate, hydrogenated cottonseed oil and hydrogenated methyl abietate in an amount between about 10% and about 50% of the combined weight of the rubber and dehydrogenated rosin.

5. An age-resistant, highly tacky, pressure-sensitive adhesive comprising. rubber, a rosin which has undergone interand intramolecular rearrangement in such manner that the ethylenic unsaturation thereof has been reduced, said rearrangement having been effected by treatment of therosin with a hydrogenation catalyst in the absence of added substances capable of reducing the degree of unsaturation thereof, the ratio of rubber to said modified rosin being between 40:60 and 80:20, and a softener selected from the group consisting of lanolin, mineral 01], glycerol tripropionate, dibutyl phthalate, hydrogenated cottonseed oil and hydrogenated methyl abietate in an amount between about 10% and about of the combined weight of the rubber and modified rosin.

6. An age-resistant, highly tacky, pressuresensitive masking tape comprising P per coated with an adhesive comprising a rubber, a rosin which has undergone inter-and intramolecular rearrangement in such manner that the ethylenic unsaturation thereof has been reduced, said rearrangement having been eflected by treatment of the rosin with a hydrogenation catalyst in the absence of added substances capable of reducing the degree of unsaturation thereof, the ratio of rubber to said modified rosin being between 40:60 and 80:20, and a softener for the rubber-rosin derivative composition selected from the group consisting of lanolin, mineral oil, glycerol tripropionate, dlbutyl phthalate, hydrogenated cottonseed oil and hydrogenated methyl abietate in an amount between about 10% and about 50% of the combined weight of the rubber and said rosin derivative. r

7. An age-resistant, highly tacky, pressure sensitive sheeting comprising a film of regenerated cellulose coated with an adhesive comprising a rubber, a rosin which has undergone interand intramolecular rearrangement in such manner that the ethylenic unsaturation thereof has been reduced, said rearrangement having been effected by treatment of the rosin with a hydrogenation catalyst in the absence of added substances capable of reducing the degree of unsaturation thereof, the ratio of rubber to said modified rosin being between 40:60 and :20, and a softener for the rubber-rosin derivative composition'selected from the group consisting of lanolin, mineral oil, glycerol tripropionate, dibutyl phthalate, hydrogenated cottonseed oil and hydrogenated methyl abietate in an amount between about 10% and about 50% of the combined weght of the rubber and said rosin derivative.

8. An age-resistant, highly tacky, pressure-sensitive adhesive tape comprising cotton textile sheeting coated with an'adhesive comprising a rubber, a rosin which has undergone interand intramolecular rearrangement in such manner that the ethylenic unsaturation thereof has been reduced, said rearrangement having been effected by treatment of the rosin with a hydrogenation catalyst in the absence of added substances capable of reducing the degree of unsaturation thereof, the ratio of rubber to said modified rosin being between 40:60 and 80:20, and lanolin in an amount between about 10% and about 50% of the combined weight of the rubber and said modified rosin.

9. An age-resistant, highly tacky, pressure-sensitive adhesive comprising a rubber, a material selected from th group consisting of rosins, rosin acids and rosin acid esters, which have undergone mineral oil, glycerol tripropionate, dibutyl phthalate, hydogenated cottonseed oil and hydrogenated methyl abietate in an amount between about 10% and about 50% of the combined weight of the rubber and said rosin derivative.

10. An age-resistant, highly tacky, pressuresensitive adhesive sheeting comprising a base sheet coated with an adhesive comprising a rubber, a material selected from the group consisting of rosins, rosin acids and rosin acid esters, which have undergone interand intramolecular rearrangement in such manner that their ethylenic unsaturation has been reduced, said rearrangement having been effected by treatment of the material with a hydrogenation catalyst in the absence of added substances capable of reducing the degree of unsaturation; the ratio of rubber to said rosin derivative being between 40:60 and 80:20, and a softener for the-rubber-rosin derivative composition selected from the group consisting of lanolin, mineral oil, glycerol tripropionate, dibutyl phthalate, hydrogenated cottonseed oil and hydrogenated methyl abietate in an amount between about 10%. and about 50% of the combined weight of the rubber and said rosin deriveive.

EMILE PRAGOFF, JR. 

